Secondary lymphoid organs

Secondary Lymphoid Organs

Secondary lymphoid organs are specialized structures where mature lymphocytes encounter antigens and are activated to participate in the immune response. They include lymph nodes, spleen, tonsils, Peyer's patches, and mucosa-associated lymphoid tissue (MALT).

Lymph Nodes

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Diagram of a lymph node showing lymph flow

Lymph nodes are small, bean-shaped structures that produce and store cells that fight infection and disease. They are the most numerous secondary lymphoid organs and are strategically located throughout the body to filter antigens from the tissues.

Spleen

File:Spleen diagram.png

Diagram of the spleen

The spleen is the largest secondary lymphoid organ. It filters blood, removing old or damaged red blood cells and platelets and helping to detect and respond to foreign substances in the blood.

Tonsils

Tonsils are large clusters of lymphatic cells found in the pharynx. They are the body's first line of defense as part of the immune system. They sample bacteria and viruses that enter the body through the mouth or nose.

Peyer's Patches

Peyer's patches are small masses of lymphatic tissue found throughout the ileum region of the small intestine. They are important in the immune surveillance of the intestinal lumen and in the generation of the immune response to ingested substances.

Mucosa-associated lymphoid tissue (MALT)

Mucosa-associated lymphoid tissue (MALT) is a diffuse system of small concentrations of lymphoid tissue found in various submucosal membrane sites of the body, such as the gastrointestinal tract, nasopharynx, thyroid, breast, lung, salivary glands, eye, and skin. MALT is populated by lymphocytes such as T cells and B cells, as well as plasma cells and macrophages, each of which is well situated to encounter antigens passing through the mucosal epithelium.

See Also

• Primary lymphoid organ
• Immune system
• Lymphatic system